Colored lustrous pigments are known in which the colorant is selected from a wide variety of inorganic and organic coloring agents or dyestuffs and the lustrous pigment is a natural pearlescent material or synthetic pearlescent substance (also called nacreous pigments). Numerous difficulties were encountered in the prior art when making such colored lustrous pigments. For example, severe bleeding of the color on filtration of the coated product from the suspension, poor adherence of the dyestuff on the surface of the pigment such that the color could be washed off with water, difficulty in retaining luster with increased color intensity, and non-uniform distribution of the dyestuff on the pigment surface have been noted.
The foregoing is described in part in U.S. Pat. No. 4,084,983. That pigment relates to the use of titanium dioxide coated mica pigments to produce colors due to the interference phenomenon and additional color effects are achieved by coating organic dyes on the surface of those pigments. An improvement in the process of that patent is set forth in U.S. Pat. No. 4,968,351 in which is described a process of absorbing a soluble organic dyestuff at a coating pH on the surface of the metal oxide coated substrate nacreous pigment in an aqueous dispersion and subsequently absorbing a laking reagent thereon.
As apparent from the patents just described, the selection of treatment conditions to achieve a desired product can be difficult because, for example, the respective pigments and dyes have different cohesive forces. In addition, some pigments and dyes do not have sufficient dispersion stability and reaggregation of the pigment particles occurs and good coloration is not achieved.
A different approach is described in U.S. Pat. No. 5,336,309. In that patent, the platy substrate and dye are subjected to high speed stirring for a predetermined period of time in the absence of a liquid medium, for the purpose of coating the surfaces of the platy pigment with the dye by forming an "ordered mixture". This method of achieving colored lustrous pigments by high speed dry stirring or blending requires that the stirring energy imparted to the mixture be critically adapted into the components being blended. For example, Example 3 and Comparative Example 2 of the patent combined the same titanium oxide-coated mica with the same organic pigment. When the stirring energy was 84.2 kJ and the stirring speed of 70 m/sec was employed, a colored pigment with dispersibility was achieved. However, when the energy was 20.7 kJ and the stirring speed of 20 m/sec was employed, the resulting product was found to contain aggregates of the organic pigment particles.
It has now been discovered that the dry blending process can be improved if certain selected adjuvants are also employed. The resulting product has increased hydrophobicity and requires a lower amount of energy to be used in the blending step. The process improves the adherence and distribution of the dye on the pearlescent pigment and the resulting product is a stable dispersion, particularly suitable for use in cosmetic applications. The selected adjuvant eases the blending process, improves the quality and stability of the colorant dispersion and is a "value added" component of the final product.
It is therefore the object of the present invention to provide a new colored lustrous pearlescent pigment and a method by which such pigment can be manufactured. This and other objects of the invention will become apparent to those skilled in the art from the following detailed description.